Well the old cars die soon on themself. So you don't need to make the poor people even poorer. They don't need to promote solar energy, they only need to remove the bureaucracy.....just let the people do it without the huge costs of doing it alright with regulations that have no technical reason.
Easiest would be to put solar panels on large government buildings. Many of these are huge, it pays for itself and some electric is directly used there on the AC when it is produced. If there is a parking place, roof it and put electric charger for cars only during day. If doing smart solar panels in Thailand make profit after 3-4 years.
That is not enough but that is a very low hanging fruit.